Adding Access-Control-Allow-Origin header response in Laravel 5.3 Passport

Adding the Access-Control-Allow-Origin header to responses in a Laravel 5.3 application using Laravel Passport can help resolve CORS (Cross-Origin Resource Sharing) issues.

CORS issues occur when a web application attempts to make requests to a domain different from the one that served the web page.

Here are the steps and technical notes on how to add this header in a Laravel 5.3 application:

Steps to Add Access-Control-Allow-Origin Header

1. Create Middleware for CORS:

Create a new middleware that will handle the addition of CORS headers.
php artisan make:middleware CorsMiddleware

2. Edit the Middleware:

Open the newly created middleware file app/Http/Middleware/CorsMiddleware.php and add the following code:

namespace App\Http\Middleware;
use Closure;
class CorsMiddleware
{
   /**
    * Handle an incoming request.
    *
    * @param  \Illuminate\Http\Request  $request
    * @param  \Closure  $next
    * @return mixed
    */
   public function handle($request, Closure $next)
   {
       $response = $next($request);
       $response->headers->set('Access-Control-Allow-Origin', '*');
       $response->headers->set('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
       $response->headers->set('Access-Control-Allow-Headers', 'Content-Type, Authorization');


       return $response;
   }
}

3. Register the Middleware:

Register the middleware in your app/Http/Kernel.php file. Add it to the $middleware array to make it globally available or to the $routeMiddleware array to use it for specific routes.

php artisan make:middleware CorsMiddleware

Or, if you want to use it for specific routes:

protected $routeMiddleware = [
   // Other route middleware
   'cors' => \App\Http\Middleware\CorsMiddleware::class,
];

4. Use Middleware for Specific Routes:

If you added it to the $routeMiddleware array, you can use it in your routes or controllers:

Route::group(['middleware' => 'cors'], function () {
 // Your routes
});

Or in a controller:

public function __construct()
{
   $this->middleware('cors');
}

Additional Notes

Options Request Handling: For preflight requests (HTTP OPTIONS), you may need to handle them separately to ensure the CORS headers are properly returned. Add this handling to the middleware:

if ($request->isMethod('OPTIONS')) {
 $response->headers->set('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
 $response->headers->set('Access-Control-Allow-Headers', 'Content-Type, Authorization');
 return $response;
}

Security Considerations: Allowing all origins with * can pose security risks. It’s better to specify allowed origins if possible.

Debugging: If you encounter issues, use browser developer tools to inspect the network requests and responses to ensure the headers are being set correctly.